Flutter valves



P 9, 1958 L. F.-CAMPBELL ETAL 2,851,054

FLUTTER VALVES Filed Oct. 25, 1945 WW W tat

FLUTTER VALVES Lawrence F. Campbell, Silver Spring, Md., and Ralph C.Taylor, Washington, D. C.

This invention relates to valves, and more particularly to fluttervalves for gas pulsator type motors.

Essentially, a gas pulsator motor is atubular structure comprising anair scoop at the leading end, a valve system associated with the airscoop for controlling the flow of air, a combustion chamber to the rearof the valve system and a discharge tail pipe or resonating duct. As thename implies, the jet is intermittent in character and the operation ofthe whole unit is cyclical instead of continuous.

' The pressure for the acceleration of the exhaust gases is the resultof several superimposed phenomena. A small amount of ram compression isobtained due to the forward flight velocity and an additional pressurerise is obtained as a result of the pressure wave due to the resonanceof the tail pipe, but the major portion of the compression is the resultof the rapid combustion of the fuel. This rapid combustion increases thetemperature of the gases within the combustion chamber which results ina'rapid rise in pressure. The rate of combustion must be rapid,otherwise the increased temperature will result in a slow flow of gasesthrough the tail pipe without developing any significant thrust. Thevalve system enables a high pressure to be generated by the combustionand causes the thrust thereof to be delivered rearwardly.

In one type of gas pulsator type motor, in order to direct the thrustfrom the motor, a valve system comprising a large member of resilientvanes is mounted at the forward end of the motor and when an explosionoccurs, the vanes are forced into closed position thus causing the forceof the explosion to be exerted out the opposite or rear end of themotor. Thereafter the pressure of the air against the outer sides ofvalves, or flutter valves as they are often termed, resulting from theforward motion of the motor, causes the flutter valves to open and toadmit air into the firing chamber. The explosions occur very rapidly,being in some cases on the order of fifty explosions per second, andconsequently the flutter valves must respond rapidly to changes in thedirection of the pressure. For this reason thin, metal vanes areemployed which are made of a resilient material and are fixed alongtheir leading edge to a suitable support. Normally, the trailing edgesof the vanes flare outwardly slightly so that when an explosion occurs,they will be forced further outward and caused to close the entranceorifice of the tube.

In practice it has been found that the considerable heat applied to thevalves by the combustion of the fuel and the rapidity and force of theexplosions cause a rapid deterioration of the metal vanes. Thus,heretofore, the useful life of the flutter valves has been extremelyshort.

An object of the present invention is to provide a new and improvedvalve for gas pulsator type motors.

A further object of the present invention is to provide a protectivecovering for the vanes of the flutter valves used with the gas pulsatortype motor to increase the useful life of the valves.

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In accordance with one embodiment of this invention the vanes of theflutter valve are encased in a sheath of thin, flexible material havingsuitable characteristics to protect the metal vanes against impact,shock, and vibration and against the heat of combustion;

Other objects and advantages of the present invention will be apparentfrom the following drawing, wherein:

Fig. 1 is a side, elevational view of a flutter valve provided with aprotective covering in accordance with this invention; and,

Fig. 2 is a vertical sectional view taken substantially along the line2-2 of Fig. 1. 1

Referring now to the drawings it will be seen that a long, rectangular,metal plate 5 is there shown having apertures 6 formed through themidportion of either end thereof for mounting the plate in the gaspulsator motor. In the motor the vane supporting plate would be mountedwith the upper edge thereof serving as the leading edge, and ordinarilya large number of these plates would be employed. A plurality of pairsof thin, resilient, metal vanes 7 are fixed to the upper edge of thevane supporting plate 5, as by the rivets 8 shown which extendtransversely through the upper portion of the plate 5. It will beunderstood that any suitable means may be employed for attaching thevanes to the supporting plate and that while at the present time itseems most desirable to employ resilient vanes, pivotally supported,rigid vanes may also be employed. The lower portions of the metal vanes7 are flared slightly outwardly and since the vanes are made ofresilient material, the current of air moving downward, with respect tothe position of the flutter valve as shown in these drawings, will tendto cause the vanes to be pressed against the sides of the vanesupporting plate 5, thus permitting the freest possible flow of air.Upon occurrence of an explosion in the firing chamber of the motor, thegases resulting from the explosion tend to move both against the flow ofair and out the opposite end of the motor. This reversal in direction ofpressure initially permits the vanes to spread outwardly clue to theirresilience and then, as the pressure increases, to bear against thevalve supporting grid 11, thus momentarily sealing the inlet orifice ofthe motor and causing the force of the explosion to be exerted primarilyrearwardly. The impact shock resulting from the explosion and the heatresulting from the combustion of the fuel has been found to causedeterioration of the metal vanes at such a rapid rate that the usefullife of the valves heretofore has been extremely short.

In accordance with the present invention in order to extend the usefullife of the flutter valve assembly, the metal vanes are encased in asheath 9. The sheath 9 may be formed from strips cut to have a widthsubstantially equivalent to the width of a vane and a lengthsubstantially double the length of the vane. In assembling a vane on thevane supporting plate 5, a strip of fabric is folded to encase the lowerend of the vane and so that the upper edges of the strip terminatesubstantially along the upper edges of the vane. Where rivets areemployed to attach the vane to the supporting plate, the rivets are thendriven through the assembly, as clearly shown in Fig. 2.

While a strip or sheet of the sheath material is simple to apply, it isalso feasible to employ a plurality of such strips disposed side by sideon each vane, or to use strands instead of strips. Where a fabricmaterial is employed, it is desirable that the majority of strands aredisposed longitudinally of the strip so that minimum frictionalresistance is offered to the flow of air. 1

The material of which the fabric sheet 9 is formed mus be one which inaddition to being thin and flexible so that it will not substantiallyinterfere with the operation of the valve, will be substantiallyimpervious to the heat whichis applied to the valve during combustionand in addition will serve to insulate the vanes from. the heat ofcombustion. Furthermore, the sheath material must be resilient as wellas flexible so that no interference with the operation of the vanes willbe incurred. The material must have a satisfactory impact strength sothat it will be able toresist the shocks resulting from the rapid andrecurrent applications of stresses during the operation of the motor. Ithasbeen found that certain materials suchas glass, or glass cloth, whichmay be bonded with a plastic impregnant such as a silicone orpolytetrafiuorethylene, both of these impregnant' materials havingsatisfactory heat resistant characteristics, are suitable sheathmaterials. Asbestos, bentonite and various ceramic ma,- terialspossesssing the aforementioned qualities may also be employed. Ingeneral, the. sheath must be made thick enough on the one hand to affordadequate heat protection and cushioning and yet not so thick as tointerfere with the operation of the valve. In a particular case theoptimum thickness Will depend upon the size and type 'of vane.

In use it' has been found that the protective sheaths 9 serve to cushionthe shock resulting from explosion so that the impact shock applied tothe vanes is greatly softened and at the same time the sheaths protectthe metal vanes from the heat of combustion. The result has been thatthe useful life of the flutter valves is extended many times thatheretofore believed possible. A further advantage resides in the sealingaction of the sheaths: as the vanes are pressed against the valve sidesto close the orifice, the sheaths are compressed and act like gasketspreventing escape of pressure. Since any forward escape of pressureduring combustion results in the hot gases moving nearer the valve, thusincreasing the temperature in the area of the valve, preventing theescape of pressure forwardly through the valve is very effective inincreasing the useful life of the valves.

While but one embodiment of this invention has been shown and described,it will be understood that many changes and modifications may be madetherein without departing from the spirit or scope of the presentinvention.

The invention shown and described herein may be manufactured and used byor for the Government of the United States of America for governmentalpurposes without the payment of any royalties thereon or therefor.

What is claimed is:

1 A flutter valve structure for pulsator type gas motors comprising avalve seat, a thin flexible metallic vane having a leading edge and atrailing edge, cushioning heat insulating means carried by said vane inthe form of a flexible sheathing of bonded glass fabric folded aroundthe trailing edge of the vane over opposite sides of the vane andextending to near the leading edge of the vane, means securing saidfabric to the vane at the leading edge, said sheathing providingprotection for said vane against hot exploding gases and cushioning thevane against impact of the exploding gases along the vane and againstmechanical impact against said valve seat, said sheathing beingcompressible to form a gasket seal against said valve seat to preventescape of pressure fluid.

2. A flutter valve structure for pulsator type gas motors comprising avalve seat, a metallic supporting plate having a leading edge and atrailing edge, a thin flexible metallic vane having a leading edge and atrailing edge, cushioning heat insulating means carried by said vane inthe form of a continuous sheathing of bonded glass fabric folded aroundthe trailing edge of the vane over opposite sides of the vane andextending to near the leading edge, means securing said vane, sheathingand supporting plate together at their leading edges, said sheathingproviding protection for said vane against hot exploding gases andcushioning the vane against impact of the exploding gases along the vaneand against mechanical impact against said valve seat, said-sheathingbeing compressible to form a gasket seal against said valve seat toprevent escape of'pres'sure fluid.

3. A flutter valve structure as claimed in claim 2 in which the heatresistant fabric is a glass cloth impregnated withpolytetrafluorethylene.

References Cited in the file of this patent UNITED STATES PATENTS952,523 Hillegass Mar. 22, 1910 1,240,848 Hiscock Sept. 25, 1 9171,995,727 Wetherbee Mar. 26, 1935 2,161,769 Trask June 6, 1939 2,402,208Read June 18, 1946 2,408,056 Farmer Sept. 24, 1946 2,432,213 RutishauserDec. 9, 1947 2,505,757 Dunbar et a1. May 2, 1950

